Sickle cell disease (SCD) remains a poorly treated disease. Based on evidence that endothelial P-selectin is central to the abnormal microvascular blood flow in SCD, we are targeting this molecule with our therapy. Our in vitro and preliminary clinical data show that pentosan polysulfate sodium (PPS) improves microvascular blood flow in SCD. However, commercially available PPS is not a viable therapy because of its marginal oral bioavailability and limited duration of action. Our plan to develop an improved second generation PPS-2 that will overcome these limitations is precluded at this time by the lack of useful PPS assays. Creation of reliable assays will enable development and commercialization of PPS-2. SCD is an inherited disorder that afflicts millions of patients worldwide, ~100,000 in the US. Most SCD morbidity is due to abnormal blood flow, conspicuously the acute pain crises that are caused by stoppage of microvascular flow. Our overarching goal is to improve the quality of life of patients with SCD by bringing to market PPS-2 as an oral P-selectin blocking drug for long-term administration to prevent sickle red blood cell sticking to the lining of blood vessels, improve blood flow, and avert acute painful episodes. In this application we propose to create reliable assays for quantifying PPS-2 candidate compounds in plasma and determining its activity in blood. The assays will be necessary for preclinical and clinical testing and useful for clinical monitoring. The inadequacy of standard assays relates to extensive molecular heterogeneity of PPS, lack of specific PPS antibodies, and plasma substances that interfere with assays. First, we will exploit the greater homogeneity of a lower molecular weight fraction of PPS as a target for a physical quantification assay method. We will adapt hydrophilic interaction chromatography (HILIC)-MS for assaying our PPS fraction. We will test the reliability of this assay in plasma samples from experimental animals administered PPS fraction. Next we will utilize the exquisite specificity provided by human combinatorial PPS MAb, which overcomes challenges that interfering plasma substances posed for hybridoma-generated MAb and polyclonal antibodies. We will obtain from AbD Serotec a recombinant PPS MAb pair generated using phage display selection for use in a sandwich ELISA. We will test the assay for quantification of high and lower molecular weight PPS-2 candidates in plasma samples from experimental animals administered the PPS test items. Lastly, Klaus Ley of the La Jolla Institute of Allergy and Immunology will devise a microfluidics device for point-of-care functional assessment of P-selectin blocking activity in a drop of blood. Determining biological activity rather than physical concentration overcomes challenges with biological variation of PPS and allows monitoring functional activity in patients. The device will be validated by assessing P-selectin blocking activity in whole blood spiked with PPS or PPS fraction and in blood samples from mice dosed with each. This Phase I SBIR will provide the reliable quantitative and functional assays for PPS and PPS fraction necessary for PPS-2 development.